Compositions designed for use in cleaning, particularly in automatic dishwashing and laundry methods are well known and a consistent effort has been made by detergent manufacturers to improve the cleaning and/or rinsing efficiency of said compositions as reflected by many patent publications.
The general problem of the formation of deposits as spots and films on the articles in the wash/rinse, and on the dishwashing and laundry washing machine parts is well known in the art.
Whilst the general problem of deposit formation is known, a full understanding of the many facets of the problem is however still an active area of research.
A range of deposit types can be encountered. The redeposition of soils or the breakdown products thereof, which have previously been removed from the soiled articles in the washload, provides one deposit type. Insoluble salts such as calcium phosphate or carbonate, calcium fatty acid salts (lime soaps), or certain silicate salts are other common deposit types. Composite deposit types are also common. Indeed, once an initial minor deposit forms it can act as a "seeding centre" for the formation of a larger, possibly composite, deposit structure.
Deposit formation can occur on a range of commonly encountered substrate surfaces including a range of fabric types, plastic, glass, metal and china surfaces. Certain deposit types however, show a greater propensity to deposit on certain substrates. For example, lime soap deposit formation tends to be a particular problem on plastic substrates.
The formation of insoluble carbonate and phosphate, especially calcium carbonate and phosphate, deposits are a particular problem in the machine dishwashing art.
The naturally sourced, inlet water to the dishwasher machine can be a sufficient source of Ca.sup.2+ and Mg.sup.2+ ions and CO.sub.3.sup.2- /HCO.sub.3.sup.- or PO.sub.4.sup.3- ions to make deposit formation a problem. Whilst the salt softening system, through which the inlet water will pass prior to entry into the main cavity of the dishwasher machine, can be efficient at removing the naturally present Ca.sup.2+ and Mg.sup.2+ ions it is inefficient at removing the CO.sub.3.sup.2- /HCO.sub.3.sup.- or PO.sub.4.sup.3- ions which therefore enter into the wash/rinse solution.
The Applicants have now established that both the levels of Ca.sup.2+ /Mg.sup.2+ hardness ions and the levels of CO.sub.3.sup.2- /HCO.sub.3.sup.- or PO.sub.4.sup.3 ions in the wash/rinse water of the dishwasher machine are factors controlling calcium carbonate and phosphate deposit formation. Critical levels of all components must be exceeded for deposit formation to occur. These critical levels are to an extent interdependent. Thus, even in wash/rinse solutions containing high levels of one component, deposit formation will not occur in the absence of the critical level of the other component.
The Applicants have now found that deposit formation is a more noticeable problem when using tablet detergent compositions. It is believed that at least some deposit formation occurs before the builder component of the detergent composition has fully dissolved into the wash solution.
It has been surprisingly found that the problem of deposit formation may be effectively ameliorated by the inclusion of amino tricarboxylic acid (ATCA) into the wash solution during the early stages of the wash.
The Applicants have also surprisingly found that the problem of deposit formation may be further ameliorated if the ATCA is delivered to the wash solution prior to the delivery of the detergent builder component.
The Applicants further found that the more effective control of calcium carbonate and phosphate deposition can also lead to benefits in the prevention of the formation of other deposit types, particularly lime soap deposits and silicate deposits.
Lime soap deposits are most commonly encountered when the washload contains fatty soils, which naturally contain levels of free fatty acids, and when lipolytic enzymes are components of the composition. Lipolytic enzymes catalyse the degradation of fatty soils into free fatty acids and glycerol. Silicate is a common component of machine dishwashing compositions, where it is added for its china care capability.